Gas turbine engine combustors are subjected to and must meet stringent emission standards. This means that the wall cooling air needs to decrease to control emissions. A combustor can have an inner and outer liner and tiles can be used to line the walls of combustor to aid in thermal control and heat dissipation. Tiles can have operating temperatures in excess of 1150° C. and are desirable to use in such extreme operating conditions.
Securing tiles to a surface, such as the metal liner of a combustor, requires a fastening system that is capable of operating in extreme temperatures. Traditionally bolts or studs have been used to secure tiles to the liner. However, bolts and other traditional fasteners, expand relative to their thermal environment. When the bolts expand the thermal expansion can result in a loss of fastener preload and can result in gaps which leak available cooling air and degrade performance of the cooling system. Over a period of time the hardware heats and cools repeatedly, which subjects the fastening system to potential variances.
Several problems exist when using metal fasteners for ceramics. One such issue is that at elevated temperatures, such as in a gas turbine engine, the relative thermal growth between a metal fastener and the ceramic is so great that the joint invariably becomes loose. A common approach could be to minimize the distance over which the thermal mismatch is applied. But the problem remains and becomes an issue of magnitude of the thermal growth.
The issue of bolts becoming loose at elevated temperatures due to thermal growth remains an unresolved problem throughout the gas turbine, and many other, industries, where high temperatures and metal fasteners are combined. Thus, the problem of fasteners thermally expanding and causing gaps or loosing of surrounding parts is an ongoing concern that could cause damage to machinery that are operating under such conditions.
Loosening can be compensated by re-torqueing fasteners or by installing a washer to fill the void that is created between the fastener and the structure which it secures. However, in a sealed system, such as a combustor for a gas turbine engine, it is not practical to disassemble the system to re-torque fasteners or install washers to remedy the situation. It would be desirable to provide an improved fastening system that overcomes the aforementioned problems.